Again Don, it depends on where you are at. In Cozumel you can rent it right there at the Lagoon for about $10 for mask, fins, and snorkel and vest. In GC you can rent them at Edans Rock and Devils Grotto again very cheap. In more remote areas you need to bring it with you and the ship doesn't rent except to those on their excursions
AFAIK. You may wish to conside buying your own and brining it with you. Lots cleaner that way as well. <G>
Jim